1. Field of the Invention
The present invention relates to an apparatus for and a method of detecting any leakage of a hermetically sealed container, and more particularly to an apparatus for and a method of detecting a defective portion such as a pin hole and the like, if any, in the sealed portion of the hermetically sealed container which is filled with water-contained materials.
2. Description of the Prior Art
Recently hermetically sealed containers have been often used for foodstuffs and the like from a sanitation point of view or from a preserving point of view. Such a hermetically sealed container is typically formed as follows. The food is stuffed into a vessel having a flange at a periphery thereof, the vessel is then covered from above with an aluminum foil of 0.06 to 0.07 mm in thickness, and the peripheral flange portion which the vessel and the cover of the aluminum foil contact each other is heat sealed to establish a completely hermetically sealed condition. Conventionally, various inspecting methods have been adopted to examine whether or not the completely hermetically sealed condition was established. For example, a hermetically sealed container was submerged in water under a reduced pressure condition. When a pin hole existed on the container, the air in the container was released into the water and appeared as air bubbles, so that they were visually observed. However, this method is not applicable to all type of the things. As the case may be, there are some type of things which can not be submerged into the water. Adoption of the vacuum pressure of 20 Torr or less to produce the pressure reduced condition also presents a problem that it becomes difficult to discriminate the above mentioned air bubbles from those caused by the boiling of the water, with the result that the exact examination thereof can not be accomplished. According to another inspecting method, a body to be examined is put into an airtight enclosure and the pressure therein is increased or reduced, so that a change in air pressure inside the airtight enclosure is caused, when the pressure difference is detected through comparison of the changes in air pressure with those in case of a reference sample. This method can not be used for flexible containers, which change in volume.
Therefore, it is a primary object of the present invention to provide a detecting apparatus and a method which is capable of correctly and quickly detecting any defective portion of the container which is filled with water-contained materials and sealed hermetically, and if desired, the locations of the defects thereof.
It is another object of the present invention to measure water leakage from only a defective portion by eliminating the effects of water which exists in the atmosphere or on the surface of the body to be examined and is not related to the defects.
Other objects and features of the present invention will be more apparent from the following detailed description with reference to the accompanying drawings.